Nor­phel's flat snow tanks
Flow of wis­dom

Struc­tures were more like fields of ice or shal­low pools that could store wa­ter Reser­voirs had to be con­structed only in ar­eas fac­ing north to get lim­ited ex­po­sure to sun­light Needed a lot of labour to con­struct th­ese struc­tures